This invention relates to a combustion control system for an internal combustion engine and more particularly to a combustion control system for improving engine characteristics in acceleration, idle and deceleration.
In an outboard motor, for example, there is a need to improve acceleration characteristics from an idle state, for example, in a trolling state, to a high engine rotation speed, which requires a rapid increase of an engine rotation. For such acceleration, it is necessary to supply a large amount of air to the engine in response to an accelerator of the motor. However, in a conventional engine, even though a throttle valve is fully opened within a very short period of time, because of an inertia effect of air, it is not possible to introduce sufficient air corresponding to the throttle opening to an inside of the engine within a short period of time. Therefore, there is a limit in the conventional engine to rapidly increase the acceleration.
It is, therefore, a principal object of the present invention to provide an improved combustion control system for an internal combustion engine that is capable of rapidly increasing the engine acceleration from an idle state by providing an increased air flow and flow rate through the throttle valve in the idle state.
According to the present invention, the combustion control system for an engine is so arranged that a throttle valve is substantially opened even in an idle state to provide an sufficient air flow to the engine in response to the fast change-over from the idle to the acceleration. However, in such a situation, since the air flow rate and the air flow velocity are relatively higher in the idle state, the engine rotation rate inevitably becomes higher during the idle. To lower the engine rotation rate in such a situation, in the present invention, ignition timing in the engine is controlled to be fully retarded during the idle. However, since the timing retard tends to be emphasized when the engine is decelerated, what is called a backfire is created, which may be uncomfortable to a user.
It is, therefore, a further object of the present invention to provide a combustion control system that has a fuel injector which is controlled such that a lower rotation speed in the engine is maintained in the idle state even when the throttle valve is substantially opened.
It is a further object of the present invention to provide a combustion control system that has a fuel injector which is controlled to selectively cease fuel injection for one or more cylinders of the engine when the engine is in the idle state.
It is a further object of the present invention to provide a combustion control system for an engine which is capable of suppressing a backfire of the engine when the engine is decelerated.
It is a further object of the present invention to provide a combustion control system for an engine which is capable of controlling a rate of change in a retard ignition timing based on the rotation rate of the engine, the ignition timing and other physical parameters.
It is a further object of the present invention to provide a combustion control system for an engine which is capable of suppressing a backfire of the engine in the deceleration state by controlling a fuel injector so that an air-fuel ratio is increased.